TypeScript support for custom commands in Cypress

Introduction

Custom commands help you reuse test steps easily. Using TypeScript makes sure your commands are checked for mistakes before running tests.

You want to create a shortcut for a repeated test action, like logging in.

You want to add new commands to Cypress that fit your app's needs.

You want your custom commands to have clear types and auto-complete in your editor.

You want to avoid mistakes by checking command inputs and outputs before running tests.

Syntax

Cypress

declare namespace Cypress {
  interface Chainable {
    customCommand(param: string): Chainable<Element>;
  }
}

Cypress.Commands.add('customCommand', (param) => {
  // command implementation
});

Use declare namespace Cypress to add types for your commands.

Define your command inside interface Chainable with input and output types.

Examples

This example adds a login command with typed email and password parameters.

Cypress

declare namespace Cypress {
  interface Chainable {
    login(email: string, password: string): Chainable<Element>;
  }
}

Cypress.Commands.add('login', (email, password) => {
  cy.get('#email').type(email);
  cy.get('#password').type(password);
  cy.get('button[type=submit]').click();
});

This example adds a selectItem command to click an item by name.

Cypress

declare namespace Cypress {
  interface Chainable {
    selectItem(itemName: string): Chainable<Element>;
  }
}

Cypress.Commands.add('selectItem', (itemName) => {
  cy.contains(itemName).click();
});

Sample Program

This test adds a greet command that logs a greeting message. The test calls cy.greet('Alice') and you will see the greeting in the test log.

Cypress

/// <reference types="cypress" />

declare namespace Cypress {
  interface Chainable {
    greet(name: string): Chainable<Element>;
  }
}

Cypress.Commands.add('greet', (name) => {
  cy.log(`Hello, ${name}!`);
});

describe('Custom Command Test', () => {
  it('uses the greet command', () => {
    cy.greet('Alice');
  });
});

Important Notes

Always add /// <reference types="cypress" /> at the top for TypeScript support.

Put your type declarations in a cypress/support/index.d.ts or similar file.

Use Chainable<Element> as the return type for commands that continue Cypress chaining.

Summary

Custom commands let you reuse test steps easily.

TypeScript support helps catch errors early and improves editor help.

Declare your commands in the Cypress.Chainable interface for typing.

Practice

1. What is the main benefit of adding TypeScript support for custom commands in Cypress?

easy

A. It makes tests run faster by optimizing command execution.

B. It provides type checking and better editor autocomplete for custom commands.

C. It automatically generates test reports for custom commands.

D. It allows running tests on multiple browsers simultaneously.

Solution

1. Step 1: Understand TypeScript role in Cypress

   TypeScript adds static type checking and editor support to catch errors early.

2. Step 2: Identify benefit for custom commands

   Typing custom commands improves autocomplete and prevents mistakes when using them.

3. Final Answer:

   It provides type checking and better editor autocomplete for custom commands. -> Option B

4. Quick Check:

   TypeScript support = type checking + autocomplete [OK]

Hint: TypeScript helps catch errors before running tests [OK]

Common Mistakes:

• Confusing TypeScript support with test speed improvements
• Thinking it auto-generates reports
• Believing it enables multi-browser runs

2. Which is the correct way to declare a custom command with TypeScript support in Cypress?

easy

A. namespace Cypress { interface myCommand { Chainable(): void } }

B. interface Cypress { Chainable { myCommand(): void } }

C. declare interface Cypress { myCommand(): void }

D. declare namespace Cypress { interface Chainable { myCommand(): Chainable<void> } }

Solution

1. Step 1: Recall TypeScript declaration syntax for Cypress commands

   Custom commands are declared inside the Cypress namespace extending Chainable interface.

2. Step 2: Match correct syntax

   declare namespace Cypress { interface Chainable { myCommand(): Chainable<void> } } correctly uses 'declare namespace Cypress' and extends 'Chainable' with 'myCommand'.

3. Final Answer:

   declare namespace Cypress { interface Chainable { myCommand(): Chainable<void> } } -> Option D

4. Quick Check:

   Namespace + Chainable interface = correct declaration [OK]

Hint: Custom commands extend Cypress.Chainable interface inside namespace [OK]

Common Mistakes:

• Missing 'declare' keyword
• Incorrect interface or namespace nesting
• Placing method outside Chainable interface

3. Given this TypeScript declaration for a custom command:

declare namespace Cypress {
  interface Chainable {
    login(email: string, password: string): Chainable<void>
  }
}

What is the correct way to use this login command in a test?

medium

A. cy.login(['[e-mail]', 'pass123'])

B. cy.login(email: '[e-mail]', password: 'pass123')

C. cy.login('[e-mail]', 'pass123')

D. cy.login()

Solution

1. Step 1: Understand method signature

   The login command takes two string arguments: email and password.

2. Step 2: Match correct usage syntax

   cy.login('[e-mail]', 'pass123') calls login with two string arguments in order, matching the declaration.

3. Final Answer:

   cy.login('[e-mail]', 'pass123') -> Option C

4. Quick Check:

   Method call with two string args = correct usage [OK]

Hint: Pass arguments as ordered parameters, not as object or array [OK]

Common Mistakes:

• Using named parameters syntax (not valid in JS calls)
• Passing arguments as array instead of separate params
• Calling without required arguments

4. You wrote this custom command declaration:

declare namespace Cypress {
  interface Chainable {
    clickButton(): void
  }
}

But when you use cy.clickButton() in your test, TypeScript shows an error. What is the problem?

medium

A. The return type should be Chainable<void>, not void.

B. The method name cannot be clickButton.

C. Custom commands must be declared outside the Cypress namespace.

D. You forgot to import Cypress in the test file.

Solution

1. Step 1: Check return type for custom commands

   Custom commands should return Chainable<T> to allow chaining in Cypress.

2. Step 2: Identify mismatch causing TypeScript error

   Returning void breaks chaining and causes TypeScript to complain.

3. Final Answer:

   The return type should be Chainable<void>, not void. -> Option A

4. Quick Check:

   Custom commands must return Chainable for chaining [OK]

Hint: Custom commands return Chainable, not void [OK]

Common Mistakes:

• Using void return type instead of Chainable
• Declaring commands outside Cypress namespace
• Assuming method names are restricted

5. You want to create a custom command fillForm that accepts an object with optional name and email fields. How should you declare it in TypeScript to support chaining and optional properties?

hard

A. declare namespace Cypress { interface Chainable { fillForm(data: { name?: string; email?: string }): Chainable<void> } }

B. declare namespace Cypress { interface Chainable { fillForm(data: { name: string; email: string }): void } }

C. declare namespace Cypress { interface Chainable { fillForm(data?: { name: string; email: string }): Chainable<void> } }

D. declare namespace Cypress { interface Chainable { fillForm(data: { name: string; email?: string }): Chainable<string> } }

Solution

1. Step 1: Define optional properties correctly

   Use question marks (?) to mark properties as optional in the data object.

2. Step 2: Ensure return type supports chaining

   Return type must be Chainable<void> to allow chaining in Cypress tests.

3. Final Answer:

   declare namespace Cypress { interface Chainable { fillForm(data: { name?: string; email?: string }): Chainable<void> } } -> Option A

4. Quick Check:

   Optional props + Chainable return = correct declaration [OK]

Hint: Use '?' for optional props and Chainable<void> return [OK]

Common Mistakes:

• Forgetting '?' for optional properties
• Using void return type instead of Chainable
• Returning wrong Chainable generic type